Field of the Invention
The present invention relates to a method for manufacturing a solid-state image sensor.
Description of the Related Art
A solid-state image sensor includes, for example, a semiconductor substrate which includes a photoelectric conversion portion, and a structure arranged on the semiconductor substrate and including an insulating member and a metal interconnection arranged in the insulating member. The insulating member is generally made of a plurality of layers where interlayer insulating layers and anti-diffusion layers for preventing diffusion of a metal from the metal interconnection are formed alternately. Silicon oxide is typically used for the interlayer insulating layers. Silicon nitride or the like can be used for the anti-diffusion layers. It is more preferable, however, that silicon carbide smaller than silicon nitride in a relative dielectric constant is used.
Some solid-state image sensors further include light-guide portions formed in positions above photoelectric conversion portions. Each light-guide portion guides light which has passed through an optical element such as a microlens to the photoelectric conversion portion. Each light-guide portion is obtained by, for example, forming an opening in the above-described insulating member, and then forming a transparent member made of silicon nitride or the like in this opening. The transparent member is formed at a relatively high temperature by a deposition method such as plasma CVD.
When forming each light-guide portion, a temperature change may cause a stress between the respective layers of the insulating member. In particular, some layers may be separated because a difference in a thermal expansion coefficient is large between silicon oxide of the interlayer insulating layers and silicon carbide of the anti-diffusion layers. This causes a reduction in quality of the solid-state image sensor.